A wide variety of systems exist for detecting and/or imaging an object of interest. Detecting an object of interest generally involves determining the absence or presence of the object, while imaging involves obtaining an electronic representation of the object based on light emanating or being reflected from the object. Additionally, often times there is value in monitoring the displacement of part of the surface of the object.
Wavelength-dependent imaging is one technique for imaging or detecting an object, and typically involves detecting one or more particular wavelengths that reflect off, or transmit through, the object. In some implementations, only solar or ambient illumination is required, while in other implementations additional illumination is needed. Light is transmitted through the atmosphere at many different wavelengths, including visible and non-visible wavelengths. Thus, the wavelengths of interest may not be visible.
When a light emitting diode (LED) or laser is used by the imaging system to illuminate the object of interest, the simultaneous presence of broad-spectrum solar radiation can make detecting light emitted from an LED or laser and reflected off an object quite challenging during the day. Solar radiation can dominate the detection system and render the relatively weak scatter from the light source small by comparison. Other ambient sources that emit radiation in the same waveband as the LED or laser may also cause such problems.
Additionally, the object being detected may not remain stationary during successive measurements. For example, if a human being is the object, the person may shift position or move during the time the measurements are taken. If measurements made at different wavelengths are made at different times, movement of the object during successive measurements can distort the measurements and render them useless.
A need exists for a way to accurately image an object to determine the surface displacement that overcomes the difficulties associated with the presence of ambient light and/or motion of the object.